#include<bits/stdc++.h>
#define i64 long long
#define ull unsigned long long
using namespace std;

const int N = 1e6 + 10, INF = 0x3f3f3f3f;

void solve()
{
    int n;
    cin >> n;
    i64 sum = 1500;
    for (int i = 0; i < n; i++)
    {
        i64 x;
        cin >> x;
        sum += x;
        if (sum >= 4000)
        {
            cout << i + 1;
            return;
        }
    }
    cout << -1;

}

signed main()
{
    //ios::sync_with_stdio(0);
    //cin.tie(0);cout.tie(0);
#define ONLINE_JUDGE
#ifndef ONLINE_JUDGE
    std::istringstream in(R"()");
    std::cin.rdbuf(in.rdbuf());
#endif
    int T = 1;
    //cin>>T;
    for (int i = 1;i <= T;i++) {
        solve();
    }
}